Owing to the lack of target-directed therapies, triple-negative breast cancer (TNBC) is difficult to effectively treat. In this article, a novel organometallic histone deacetylase (HDAC) inhibitor, Fc-SelSA, based on the selenocyanide (SelSA) zinc-binding motif, was synthesized using a ferrocenyl group as the cap to confer activity against TNBC. The synthesized Fc-SeISA was evaluated for bioactivity in vitro and in vivo. An enzymatic assay showed that Fc-SeISA was a potent HDAC inhibitor with a half-maximum inhibitory concentration (IC50) of 14.8 nM. Molecular docking studies of Fc-SelSA with HDAC suggested that the ferrocenyl unit overlaps with the phenyl group of suberoylanilide hydroxamic acid (SAHA) and the amido group of Fc-SelSA can form hydrogen bonds with the D98 and G151 residues of HDAC, but SAHA and SelSA do not show similar interactions. Moreover, Fc-SelSA reactivated the estrogen receptor alpha (ER alpha) expression, sensitized TNBC cells to the antagonist tamoxifen, and exerted more potent antitumor effects against TNBC MDA-MB-231 tumor xenografts in comparison to SelSA with no obvious side effects. Our results indicate that Fc-SeISA is a potent oral anticancer candidate for HDAC-targeted TNBC therapy and deserves further investigation for clinical application.